ancestor.missingancestors: turn into a state-keeping class

This allows multiple efficient missing ancestor queries against the same set of
bases. In upcoming patches we'll also define ways to grow the set of bases.

The fact that the test output hasn't changed establishes this patch's
correctness.

mercurial/ancestor.py

@@ -134,83 +134,95 b' def ancestors(pfunc, *orignodes):'
         return gca
     return deepest(gca)
 
-def missingancestors(revs, bases, pfunc):
-    """Return all the ancestors of revs that are not ancestors of bases.
-
-    This may include elements from revs.
+class incrementalmissingancestors(object):
+    '''persistent state used to calculate missing ancestors incrementally
 
-    Equivalent to the revset (::revs - ::bases). Revs are returned in
-    revision number order, which is a topological order.
-
-    revs and bases should both be iterables. pfunc must return a list of
-    parent revs for a given revs.
-    """
+    Although similar in spirit to lazyancestors below, this is a separate class
+    because trying to support contains and missingancestors operations with the
+    same internal data structures adds needless complexity.'''
+    def __init__(self, pfunc, bases):
+        self.bases = set(bases)
+        if not self.bases:
+            self.bases.add(nullrev)
+        self.pfunc = pfunc
 
-    revsvisit = set(revs)
-    basesvisit = set(bases)
-    if not basesvisit:
-        basesvisit.add(nullrev)
-    bothvisit = revsvisit.intersection(basesvisit)
-    revsvisit.difference_update(bothvisit)
-    if not revsvisit:
-        return []
-    start = max(max(revsvisit), max(basesvisit))
-    # At this point, we hold the invariants that:
-    # - revsvisit is the set of nodes we know are an ancestor of at least one
-    #   of the nodes in revs
-    # - basesvisit is the same for bases
-    # - bothvisit is the set of nodes we know are ancestors of at least one of
-    #   the nodes in revs and one of the nodes in bases, and that are smaller
-    #   than curr. bothvisit and revsvisit are mutually exclusive, but bothvisit
-    #   is a subset of basesvisit.
-    # Now we walk down in reverse topo order, adding parents of nodes already
-    # visited to the sets while maintaining the invariants. When a node is found
-    # in both revsvisit and basesvisit, it is removed from revsvisit and added
-    # to bothvisit. When revsvisit becomes empty, there are no more ancestors of
-    # revs that aren't also ancestors of bases, so exit.
+    def missingancestors(self, revs):
+        '''return all the ancestors of revs that are not ancestors of self.bases
+
+        This may include elements from revs.
 
-    missing = []
-    for curr in xrange(start, nullrev, -1):
+        Equivalent to the revset (::revs - ::self.bases). Revs are returned in
+        revision number order, which is a topological order.'''
+        revsvisit = set(revs)
+        basesvisit = self.bases
+        pfunc = self.pfunc
+        bothvisit = revsvisit.intersection(basesvisit)
+        revsvisit.difference_update(bothvisit)
         if not revsvisit:
-            break
+            return []
 
-        if curr in bothvisit:
-            bothvisit.remove(curr)
-            # curr's parents might have made it into revsvisit through another
-            # path
-            for p in pfunc(curr):
-                revsvisit.discard(p)
-                basesvisit.add(p)
-                bothvisit.add(p)
-            continue
+        start = max(max(revsvisit), max(basesvisit))
+        # At this point, we hold the invariants that:
+        # - revsvisit is the set of nodes we know are an ancestor of at least
+        #   one of the nodes in revs
+        # - basesvisit is the same for bases
+        # - bothvisit is the set of nodes we know are ancestors of at least one
+        #   of the nodes in revs and one of the nodes in bases. bothvisit and
+        #   revsvisit are mutually exclusive, but bothvisit is a subset of
+        #   basesvisit.
+        # Now we walk down in reverse topo order, adding parents of nodes
+        # already visited to the sets while maintaining the invariants. When a
+        # node is found in both revsvisit and basesvisit, it is removed from
+        # revsvisit and added to bothvisit. When revsvisit becomes empty, there
+        # are no more ancestors of revs that aren't also ancestors of bases, so
+        # exit.
+
+        missing = []
+        for curr in xrange(start, nullrev, -1):
+            if not revsvisit:
+                break
 
-        if curr in revsvisit:
-            missing.append(curr)
-            revsvisit.remove(curr)
-            thisvisit = revsvisit
-            othervisit = basesvisit
-        elif curr in basesvisit:
-            thisvisit = basesvisit
-            othervisit = revsvisit
-        else:
-            # not an ancestor of revs or bases: ignore
-            continue
+            if curr in bothvisit:
+                bothvisit.remove(curr)
+                # curr's parents might have made it into revsvisit through
+                # another path
+                for p in pfunc(curr):
+                    revsvisit.discard(p)
+                    basesvisit.add(p)
+                    bothvisit.add(p)
+                continue
 
-        for p in pfunc(curr):
-            if p == nullrev:
-                pass
-            elif p in othervisit or p in bothvisit:
-                # p is implicitly in thisvisit. This means p is or should be
-                # in bothvisit
-                revsvisit.discard(p)
-                basesvisit.add(p)
-                bothvisit.add(p)
+            if curr in revsvisit:
+                missing.append(curr)
+                revsvisit.remove(curr)
+                thisvisit = revsvisit
+                othervisit = basesvisit
+            elif curr in basesvisit:
+                thisvisit = basesvisit
+                othervisit = revsvisit
             else:
-                # visit later
-                thisvisit.add(p)
+                # not an ancestor of revs or bases: ignore
+                continue
 
-    missing.reverse()
-    return missing
+            for p in pfunc(curr):
+                if p == nullrev:
+                    pass
+                elif p in othervisit or p in bothvisit:
+                    # p is implicitly in thisvisit. This means p is or should be
+                    # in bothvisit
+                    revsvisit.discard(p)
+                    basesvisit.add(p)
+                    bothvisit.add(p)
+                else:
+                    # visit later
+                    thisvisit.add(p)
+
+        missing.reverse()
+        return missing
+
+def missingancestors(revs, bases, pfunc):
+    inc = incrementalmissingancestors(pfunc, bases)
+    return inc.missingancestors(revs)
 
 class lazyancestors(object):
     def __init__(self, pfunc, revs, stoprev=0, inclusive=False):

tests/test-ancestor.py

@@ -88,7 +88,8 b' def test_missingancestors(seed, rng):'
             revs = samplerevs(graphnodes)
 
             # fast algorithm
-            h = ancestor.missingancestors(revs, bases, graph.__getitem__)
+            inc = ancestor.incrementalmissingancestors(graph.__getitem__, bases)
+            h = inc.missingancestors(revs)
             # reference slow algorithm
             r = naivemissingancestors(ancs, revs, bases)
             if h != r: